The movie was filmed largely with small, handheld Canon cameras. Several weeks of production were done within an actual submarine that is part of a private collector's fleet. Read more here.\
The Submarine used is moored at Rochester UK, its an ex Soviet U-475 Cold War submarine that previously served as museum at different locations in UK. It was launched in 1967 and decommissioned in 1993. Its still got its original torpedos inside which have been disarmed. She is privately owned and currently undergoing refurbishment.
